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Fossils reveal the color of extinct species, study finds

Researchers have discovered fossils that contain pigment molecules, revealing the color of animals that have been extinct for millions of years.

Researchers from Virginia Tech and the University of Bristol have shown a method for extracting pigment from mammalian fossils, revealing the true color of species that have been extinct for millions of years. According to a press release from Eurekalert, the study shows that the color of two bat species that have been extinct for roughly 50 million years were likely a reddish brown color, marking the first time scientists have been able to accurately determine an extinct specie’s shade.

The techniques outlined in the study can be used to determine the color of animals with well-preserved fossils dating back at least 300 million years. According to Caitlin Colleary, a doctoral student of geoscience at the College of Science at Virginia Tech, her colleagues and she have studied tissues from fish, frogs, tadpoles, the hair from mammals, birds’ feathers, and octopus and squid ink. Each of these samples preserves melanin, which appears throughout the majority of the fossil record. Using this information, Colleary and her team were able to fill in gaps in the color patterns of some truly ancient animals.

Colleary collaborated with scientists from the United Kingdom, Germany, Ethiopia, and Denmark to present her findings in the Proceedings of the National Academy of Sciences. The scientists revealed that tiny structures which were long believed to be fossilized bacteria are actually melanosomes, or organelles that contain melanin, the pigment in hair, feather, skin, and eye cells that produce pigment.

Fossilized melanosomes were first discovered in a fossil feather by Jakob Vinther, a molecular paleobiologist from the University of Bristol in 2008. Vinther was the senior author of the most recent study. Since this discovery, the shape of melanosomes have been used to determine how marine reptile species are related, and what color many species of dinosaurs likely were.

“Very importantly, we see that the different melanins are found in organelles of different shapes: reddish melanosomes are shaped like little meatballs, while black melanosomes are shaped like little sausages and we can see that this trend is also present in the fossils,” Vinther explained. “This means that this correlation of melanin color to shape is an ancient invention, which we can use to easily tell color from fossils by simply looking at the melanosomes shape.”

Melanosomes are chemically unique as well, and an instrument called a time-of-flight secondary ion mass spectrometer can help researchers identify the molecular composition of melanosomes to compare with modern specimens.

Researchers also replicated the conditions under which the fossils were formed to see how much the chemical composition of melanin had changed over time. They placed modern feathers under extreme heat and pressure to understand what happens to melanosomes’ chemical makeup during the millions of years it would have taken for them to become fossils.

“By incorporating these experiments, we were able to see how melanin chemically changes over millions of years, establishing a really exciting new way of unlocking information previously inaccessible in fossils,” Colleary said.

The research was primarily conducted at the University of Bristol, where Colleary worked as a Master’s student with Vinther, as well as at the University of Texas at Austin. It received funding from UT Austin, National Geographic, and the University of Bristol.

According to Roger Summons, the Schlumberger Professor of Earth Science at the Massachusetts Institute of Technology, who did not play a role in the research, “It was important to bring microchemistry into the debate, because discussion has been going on for years over whether these structures were just fossilized bacteria or specific bodies where melanin is concentrated. These two things have very different chemical compositions.”

Summons was involved in previous research that examined how the fossils of squid showed ink from the Jurassic period that was chemically identical to ink from modern cuttlefish. The recent study helps explain the evolution of all living things on Earth.

“How color is imparted and how we characterize it in fossils are important, because they inform us about a very specific aspect of the history of life on our planet,” the professor explained. “For complex animal life, color is a factor in how individuals recognize and respond to others, determine friend or foe, and find mates. This research provides another thread to understand how ancient life evolved. Color recognition was an important part of that process, and it goes far back in the history of animals.”